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In today’s era of pursuing sustainable development and clean energy, wood pellets are gradually gaining widespread attention as an environmentally friendly and efficient energy product. So how exactly are wood pellets made?
Characteristics and advantages of wood pellets
Wood pellets, also known as biomass pellets, are mainly produced from wood processing residues such as sawdust, wood shavings, branches, etc. through a series of processes. It has the following significant advantages:
- The environmental protection is excellent. Wood pellets produce relatively few pollutants in the combustion process, and their carbon dioxide emissions are close to zero, because the carbon dioxide absorbed by wood during growth is approximately equal to the carbon dioxide released during combustion. At the same time, it produces almost no harmful gases such as sulfur dioxide, which has a minimal impact on air quality.
- High energy efficiency. Wood pellets have a high calorific value and can provide stable heat output, which can be widely used in home heating, industrial boilers and other fields.
- Strong sustainability. Wood is a renewable resource, and as long as it is properly managed and harvested, it can provide a continuous supply of raw materials for wood pellet production.
Advantages of wood pellets
what are pellets made of
- In the process of wood processing, a large amount of sawdust, wood shavings and wood chips are produced. Sawdust is a fine-grained material produced when sawing wood, its texture is more uniform, rich in cellulose and lignin, is one of the high-quality raw materials for the production of wood pellets. Wood chips, on the other hand, are usually produced during wood cutting and sanding processes, and their particles are of different sizes, which can be used in the production of wood pellets after screening and treatment. Wood chips can be leftovers from wood harvesting or initial processing, which can be converted into material suitable for wood pellet production through further pulverization.
- The furniture industry is also a rich source of raw material for the production of wood pellets. Furniture offcuts, such as strips and blocks, come in a variety of sizes and shapes, but after sorting and processing, they can be effective ingredients for wood pellet production.
- Waste wood from the construction industry can also be used to make wood pellets. Waste wood squares and waste stencils can be converted into raw materials for wood pellets after removal of impurities, nails and other treatments, as well as crushing and drying.
- In addition, forest residues such as branches and tree tops are also important components of wood pellets. Branches and tree tops are often considered waste in the logging industry, but with proper collection and processing, they can become valuable raw materials for wood pellets. These logging residues usually contain high levels of moisture and need to be adequately dried to ensure the quality and burning properties of wood pellets.
what are pellets made of
Raw material requirements for making wood pellets
- First, the moisture content of the feedstock is critical. In general, the moisture content of wood pellet feedstock should be controlled within a certain range, usually between 10% and 15%. Too much moisture can make it difficult to shape the pellets during the production process, the pellets will tend to loosen, and mold can form during storage, reducing the quality and combustion properties of the wood pellets. On the contrary, if the moisture is too low, it will increase the production cost and may make the pellets too dry during the production process and produce dust, which will affect the production environment and the health of the operators.
- Second, the size of the raw material should be as uniform as possible. Too large particles must be crushed, which not only increases the production process and energy consumption, but can also affect the density and strength uniformity of the particles. Too small particles, on the other hand, may cause dust in the production process, but are also not conducive to stable operation of the pelletizer. Generally, the size of raw material particles should be between 3 and 5 millimeters, which is convenient for further processing and can ensure the quality of wood pellets.
- In addition, the raw material should try to avoid impurities. Sand, gravel, metal and other impurities will not only damage the production equipment such as molds and pressure rollers of the pellet mill, reducing the service life of the equipment, but also may produce harmful substances in the combustion process, affecting the environmental performance of wood pellets. At the same time, the presence of impurities will also reduce the calorific value and combustion efficiency of wood pellets.
- Finally, there are certain requirements for the types of raw materials. Different types of wood have different chemical compositions and combustion characteristics, so consistency should be maintained as much as possible when selecting feedstocks. Some hardwood feedstocks can give wood pellets higher density and strength, but the corresponding production costs may also increase. Softwood feedstocks, on the other hand, are less expensive but may be slightly less effective in terms of combustion properties and durability.
Process flow and equipment configuration for making wood pellets
- The process starts with the collection of raw materials. Wood processing waste, furniture trimmings, construction waste wood and forest logging waste are widely collected as raw materials. The raw materials are then screened to remove impurities such as sand, stone, metal, etc. to ensure the purity of the raw materials.
- This is followed by pulverization, where larger-sized materials such as wood chips and branches are reduced to smaller particles, typically between 3 and 5 mm, using a pulverizer. This step increases the surface area of the raw material and creates favorable conditions for subsequent processing.
- The shredded material is then dried. Using equipment such as a drum dryer, the drying temperature and time are tightly controlled to reduce the moisture content of the raw material to the appropriate range, typically 10% – 15%, to ensure smooth pellet formation during the production process.
- This is followed by the critical pelletizing stage. In this stage, a pelletizer is used to compress the dried material into pellets by extrusion and friction. During the process, parameters such as pressure, temperature, and speed must be precisely controlled so that the pellets have the required density, strength, and shape, typically cylindrical, between 10 – 30 mm in length, with a density of 1 – 1.2 g/cm3 and a strength of more than 95%.
- Freshly manufactured wood pellets are hot and must be cooled. This can be done naturally or by using cooling equipment such as cooling towers, fans, etc. to speed up the cooling process. The cooled particles are then screened to remove broken particles and impurities to ensure product quality.
- In terms of equipment configuration, the pulverizer is essential, and its performance determines the efficiency and quality of raw material pulverization. Drum dryer is used to accurately control the moisture content of raw materials.
- Granulator as the core equipment, its power, performance and stability directly affect the pellet forming effect. In addition, cooling equipment and screening equipment also play an important role in ensuring that the final product is of excellent quality.
Wood shaving
Prospects for the application of wood pellets
With the increasing global emphasis on environmental protection and sustainable development, wood pellets, as a clean and renewable energy product, have a wide range of applications. In the field of home heating, wood pellets can replace traditional fossil fuels such as coal and oil, reduce the emission of pollutants and improve the efficiency of energy use. In the field of industrial boilers, wood pellets can be used as a new type of fuel to reduce the energy costs of enterprises while meeting the requirements of environmental protection. In addition, wood pellets can also be used in power generation, chemical industry and other fields, providing strong support for sustainable economic and social development.
In conclusion, the production of wood pellets is a work of great importance. Through reasonable raw material selection, strict process and quality control, we can produce high quality wood pellets, contributing to environmental protection and sustainable energy development. We believe that in the future, wood pellets will be widely used in more fields and become an important force to promote economic and social development.
